Certainly! The guidelines and regulations for visual inspection of liquid oral preparations are aimed at ensuring the safety and quality of pharmaceutical products. Here are some references from reputable regulatory authorities:

1. WHO (World Health Organization): "Good Manufacturing Practices: Main Principles for Pharmaceutical Products" - This document provides detailed guidance on the principles of good manufacturing practices, including visual inspection requirements for pharmaceutical products.

2. USFDA (United States Food and Drug Administration): "Guidance for Industry: Container and Closure System Integrity Testing in Lieu of Sterility Testing as a Component of the Stability Protocol for Sterile Products" - This guidance provides information on container and closure system integrity testing, which may include visual inspection.

3. MHRA (Medicines and Healthcare products Regulatory Agency) - "Orange Guide" - The Orange Guide contains regulations and guidelines for pharmaceutical products including visual inspection requirements for liquid oral preparations.

4. EU (European Union): "EudraLex - Volume 4 - Good Manufacturing Practice (GMP) Guidelines" - This volume of EudraLex provides guidance on GMP including visual inspection requirements for pharmaceutical products.

5. ANVISA (Agência Nacional de Vigilância Sanitária): "Resolução da Diretoria Colegiada - RDC No. 17, de 16 de abril de 2010" - This resolution contains guidelines for the registration of medicines, including requirements for visual inspection of liquid oral preparations.

These references from regulatory authorities provide comprehensive guidelines and regulations for the visual inspection of liquid oral preparations to ensure their safety and quality.